1. Field of the Invention
This invention relates to a portable information terminal apparatus having the functions of displaying transmitting and receiving data.
2. Description of the Related Art
Conventionally, for displaying various kinds of transmitting and receiving data, a portable information terminal apparatus typified by a portable telephone normally incorporates a monochrome display unit utilizing a display device such as an LCD (Liquid Crystal Display), an EL (Electro luminescence) that is a self-emitting device, or an LED (Light Emitting Diode). However, in recent years, image data such as pictures and moving images can be transmitted easily, leading to a gradually growing demand for a full-color display in the terminal apparatus.
In order to fulfill such demands, a terminal apparatus having a display unit composed of a color LCD driven by TFTs (Thin Film Transistors) has been developed. However, in general, a color display unit requires a large amount of electric power to be driven. For this reason there has been a problem that when a terminal apparatus incorporating a color display unit is driven only by batteries, it can only be used for a short time per each charging period. This use time is shorter than the time available if a monochrome terminal apparatus is used.
To solve the above-mentioned problem, technology for such a terminal apparatus is disclosed in Japanese Patent Laid-Open Publication No. Hei. 10-200960. The terminal apparatus disclosed in the publication includes a display unit capable of displaying character data on a monochrome LCD panel and displaying image data on a color LCD panel, selectively, to reduce electric power consumption by the apparatus.
However, as for a portable information terminal apparatus typified by a portable telephone, there are strict requirements for the casing to be compact so that when used it is convenient. Therefore, when the casing incorporates a plurality of display units, the casing size will be enlarged contrary to the requirement for compactness. Then, if the size of screen for the display unit is reduced so as to reduce the bulk of the casing that incorporates a plurality of display units, the display instead loses its clarity and visibility.